Do I Need a Piston or Rotary Air Compressors?

Two of the most popular air compressor configurations are piston type and rotary screw compressors. There are several key differences between the two, most often based on how they are setup and which method is being used to compress air. 

Piston or reciprocating air compressors are by far the most common air compressors worldwide. They run on the same mechanical principle as a combustion engine — a crank turns a connecting rod, which in turn moves the piston up and down inside the cylinder head. An inlet valve lets air into the cylinder, compressing air as the piston is driven upward and converting electric energy into kinec energy during the process. Typically, these compressors are cooled with oil and release residue when the compressed air is discharged. 

Rotary air compressors, on the other hand, are typically configured with two interlocking helical rotars fit with a small gap between them. An inlet valve allows air to enter, which is then compressed in the space between both screws when they turn to reduce the volume and further increase pressure. 

There are oil-free rotary screw compressors available as well. In fact, there are some air compressors that come equipped with just one screw but, again, are fairly uncommon. 

Rotary air compressors and piston compressors - Comparison

1. Maintenance and wear and tear – In piston compressors, the wear and tear is greater due to a large number of moving parts. This results in more maintenance compared to a rotary screw processor. However, because of the simple mechanical setup of a piston compressor, it is easier to maintain and fix, despite the greater frequency of maintenance required.
   
   
2. Operating temperature, noise and vibration – Typically, a rotary compressor has lower operating temperatures than piston compressors. Friction is the lead cause for this, because the rotors in the screw compressor don’t come in contact, whereas piston rings are in constant contact with the cylinder walls, creating greater friction and raising temperatures. The former also generates less noise and vibrates lesser than the latter due to the same reason.
   
   
3. Air flow and operation time – Because of the high temperatures in a piston type compressor, it cannot be run non-stop due to the risk of overheating. Furthermore it is also typically run at only 50% of its total CFM or air flow capacity. The rotary screw compressor, however, is capable of being run continuously. You can also purchase a rotary screw compressor that is rated as close as possible to your required air flow capacity rather than one rated at double the capacity.
   
   
4. Space required and energy efficiency – Since rotary screws are encased next to one another in one chamber, the whole setup usually takes up less space than a piston compressor which requires cylinder heads for the vertical movement of the pistons. The former are also more energy efficient than the latter with fewer transmission losses as well. However, the effects are only discernable in compressors of 20 HP or more horsepower.
   
   
5. Pressure ratio and volume – The compression range is much greater on a piston configuration when compared to a rotary screw type. There is also more flexibility in terms of pressure ratio and capacity. However, in rotary compressors, while the flexibility is limited, the comparative volume capacity is much greater than that of reciprocating air compressors.
   
   
6. Oil carry-over – Piston compressors typically discharge more oil into the stream of compressed air than rotary screw compressors do. Due to the high-friction moving parts, wear-and-tear leads to more oil carry-over than in rotary screw compressors.
   
   
7. Price – Due to the above mentioned factors, the cost of a piston compressor is a lot lesser than that of a rotary screw compressor.
   
   

Now that you know the major differences between the two type of compressors – piston and rotary, and what advantages and disadvantages either brings to the table, you can make an informed investment. Before you decide either way, make sure to check out some great deals and one of the widest ranges of compressors available at our online store. If you have more questions, our air compressor experts at Compressor World will be more than happy to help you out.